Which sustainer system would you chose for your sailplane?

On Wednesday, January 13, 2016 at 5:30:05 PM UTC-6, Dave Walsh wrote:
I think there is little doubt that the FES system has lower drag
(thus better performance) than a pylon mounted electric
motor. Pylons are weight and complication that the FES just
doesn't have. With the pylon stuck out and the engine not
running the drag will be much greater than a failed FES. Failed
pylon mounted engine/props also produce turbulence at the
elevator, masking feel, not a nice scenario.
Are there performance figures for pylon mounted electric
sustainers? Do such gliders exist?
I know it's not a correct comparison (as the props are so much
larger being self launchers) but with engine out and a
windmilling prop the 18m DG800B goes from 48:1 to 16:1; the
20m Antares20E goes from 55:1 to 30:1.
Anybody have figures for a failed FES? I'd guess the glide
angle would still be pretty good.
Dave Walsh

If the FES fails, the blades fold back. Or, don't unfold in the first place. Only drag penalty would be on an SH if it didn't align so the nose cone isn't faired with the fuselage behind it. That is another part of the beauty of the FES.

Steve Leonard

On Wednesday, January 13, 2016 at 3:30:05 PM UTC-8, Dave Walsh wrote:
I think there is little doubt that the FES system has lower drag
(thus better performance) than a pylon mounted electric
motor. Pylons are weight and complication that the FES just
doesn't have. With the pylon stuck out and the engine not
running the drag will be much greater than a failed FES.
Dave Walsh

Dave,

I don't think so. A small prop is not as efficient as a large prop. In terms of thrust, it's better to move a lot of air slowly than a small amount of air faster. The Wright brothers got that part right, big props turning slowly are most efficient. In most glider applications, a pylon allows for a larger prop that does a nose mount. So if available energy limited, a pylon mounted larger prop offers significant advantages. Other examples are the human and solar powered aircraft

With the pylon prop stowed, there is essentially no drag penalty. The same cannot be said for FES, though I don't know what any drag penalty might be. On MKIV customer contacted me because his yaw string did not stream straight back in flight but stayed off to the side. We determined it was due to flow disruption from the stowed FES blade/s. Moving the yaw string further aft on the canopy apparently solved the problem. The point being that the stowed blade was not just tripping laminar flow behind the blade (I think stowed at roughly 3 and 9 o'clock) but was influencing a much larger area, as the string was obviously at 12 o'clock. Strange.

I agree a failed FES should have less drag than a failed and still extended pylon and prop. And the risk of being stuck with an extended but non functional FES should be near zero. Whatever degree of risk, for a stuck extended pylon, one might assign, my understanding is it's fairly rare in the ASH26E community (self launch, but the idea is the same). The engine's been running, so when it's time to get rid of the noise, the battery has adequate capacity to drive the linear actuator to lower the pylon - and the actuator has an easy time of it as it's not fighting air flow as it would be when extending the pylon in flight. I imagine there have been more instances of failure to extend pylons than getting them stowed.

Well, the main problem I see with FES is that it's plain ugly. Stemme has at least found a solution that keeps the blades out of sight.

Bert
Ventus cM TW

On Wednesday, January 13, 2016 at 1:44:05 PM UTC-8, Casey wrote:
I wonder if nose cone in trailer has to be changed?


Photos of the new nose cone:

https://www.facebook.com/lzdesign.si...31887170295631

IMHO, this plus a small 4-stroke generator of 10-20 hp is the perfect system:
https://www.facebook.com/gpgliders/v...5333550523888/

No noticeable drag if it fails to start, electric reliability and extreme range due to the generator.

On Thursday, January 14, 2016 at 4:19:13 PM UTC-6, J. Nieuwenhuize wrote:
IMHO, this plus a small 4-stroke generator of 10-20 hp is the perfect system:
https://www.facebook.com/gpgliders/v...5333550523888/

No noticeable drag if it fails to start, electric reliability and extreme range due to the generator.

Looks nice, but could the drag caused by all those doors (even closed) not equal the drag of a closed FES prop?

Speaking of FES, why not have a single blade? Counterweight in the spinner (it's been around for a long time), fold the prop into a recess under the nose of the plane, cover with a door if you want to be really Gucci...

Kirk
66

Was wondering how the Arcus E's (electric motor from Lange) are selling compared to the gas engine model?

On Thursday, January 14, 2016 at 11:06:50 PM UTC, kirk.stant wrote:
On Thursday, January 14, 2016 at 4:19:13 PM UTC-6, J. Nieuwenhuize wrote:
IMHO, this plus a small 4-stroke generator of 10-20 hp is the perfect system:
https://www.facebook.com/gpgliders/v...5333550523888/

No noticeable drag if it fails to start, electric reliability and extreme range due to the generator.

Looks nice, but could the drag caused by all those doors (even closed) not equal the drag of a closed FES prop?

Speaking of FES, why not have a single blade? Counterweight in the spinner (it's been around for a long time), fold the prop into a recess under the nose of the plane, cover with a door if you want to be really Gucci...

Kirk
66

There would have to be something far wrong with the fit of aft fuselage engine doors before they caused the same drag as a FES prop. The flight test of the Lak FES that has from time to time been cited as showing minimal drag actually shows around 4-8 kph difference for the same glide angle with the vents open (as would be normal during most gliding) - about one generation of design difference. Diagram on page 7:

http://www.front-electric-sustainer....A%20FES_en.pdf

On Sunday, September 23, 2012 at 6:55:26 AM UTC+1, Luka Žnidarši� wrote:
Dear gliderpilots!

Manufacturers are not completely sure which is the way to go. So here you can vote for your favorite sustainer system:

http://www.front-electric-sustainer.com/voting.php

Thank you,

Luka

It's interesting to see all your perspectives.
Personally, instant action without trim change wins every time....
Having witnessed a number of near misses, waiting for pylon extraction/engine firing - not to mention how the added pressure to pilot workload affects judgement. Sorry, for me it's a no-brainer.
The only real issue (for me), is the matter of span/vs weight sufficient that 13.5m span is enough?

Thanks

John

The FES has an apparent advantage in higher reliability and, perhaps, lower cost, as well as less maintenance. An engine powered sustainer has a potentially longer self-retrieve distance. Jet powered sustainers have an uncertain reliability. These motors must be spun up to a very high RPM for starting. The motors themselves are not certified for aircraft use. I know of one pilot who landed out in a very bad area when his jet failed to start after 3 attempts (miraculously neither the glider or pilot suffered any damage).
I personally won't have a sustainer. I fly a lot in Utah and Nevada, and the sustainer probably won't get me over the mountain ranges I have to cross, or even get me to a landable field that may be 50+ miles away. But most pilots don't fly in this challenging environment.

Tom